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The "Y" stations tended to be of two types, for intercepting of the signals and for identifying where they were coming from. Sometimes both functions were operated at the same site, with the direction finding (D/F) hut being a few hundred metres from the main interception building, because of the need to minimise interference. The sites collected radio traffic which was then either analysed locally or if encrypted, passed for processing initially to AdmiraltyRoom 40 in London and during World War II to the Government Code and Cypher School at Bletchley Park in Buckinghamshire.

Arkley View 1943

In the Second World War a large house called "Arkley View" on the outskirts of Barnet (now part of the London Borough of Barnet) acted as a data collection centre, where traffic was collated and passed to Bletchley Park and it also acted as a Y station.[2] Many amateur radio (ham) operators supported the work of the Y stations, being enrolled as "Voluntary Interceptors".[3]

Much of the traffic intercepted by the Y stations was recorded by hand and sent to Bletchley by motorcycle couriers and later by teleprinter, over post office land lines.[4] The name derived from Wireless Interception (WI).[5] The term was also used for similar stations attached to the India outpost of the Intelligence Corps, the Wireless Experimental Centre (WEC) outside Delhi.

Specially constructed Y stations undertook direction finding on wireless transmissions. This became particularly important in the Battle of the Atlantic where locating U-boats was vital. Admiral Dönitz told his commanders that they could not be located if they limited their wireless transmissions to under 30 seconds but skilled D/F operators were able to locate the origin of their signals in as few as six seconds.

The design of land-based D/F stations preferred by the Allies in World War II was the U-Adcock system, which consisted of a small, central operators' hut that was surrounded by four 10-metre-high (33 ft) vertical aerial poles, usually placed at the four compass points. Aerial feeders ran underground and came up in the centre of the hut and were connected to a direction finding goniometer and a wireless receiver, that allowed the bearing of the signal source to be measured. In the UK some operators were located in an underground metal tank. These stations were usually in remote places, often in the middle of farmers' fields. Traces of World War II D/F stations can be seen as circles in the fields surrounding the village of Goonhavern in Cornwall.[6]